The present invention relates generally to measurement of carbon particulates, and more particularly to a method and apparatus for determining the particulate level or concentration of a sampled gas, e.g. diesel exhaust.
The quality of air has become an important environmental concern within recent years. In an effort to-curb air pollution and maintain air quality, strict vehicle exhaust emission guidelines have been set by federal and state authorities. Requirements for diesel emissions are extremely stringent because of the harmful effects of diesel exhausts within the atmosphere. Therefore, each diesel vehicle sold, for example within the United States, must pass certain emission tests and meet strict environmental emission standards. To determine if emission standards have been met, it is necessary to measure the particulate concentration of diesel exhaust. In order to accurately determine whether a diesel engine meets emission standards, a reliable reading of the particulate concentration of diesel exhaust is necessary. An inaccurate reading of diesel particulate concentration could result in a diesel engine improperly passing or failing emission tests. It is, therefore, desirable to utilize a technique for accurately and reliably measuring the particulate concentration of diesel exhaust.
Presently, diesel particulate is measured using a few different types of systems. One particular technique involves a direct measurement of the mass of particulate within exhaust on a real-time basis. With this technique a tapered element oscillating microbalance such as that shown in U.S. Pat. No. 4,391,338 is capable of measuring the mass of particulate deposited on a filter. This technique is not inexpensive and generally requires a dilution tunnel for proper use. Another technique for measuring the amount of particulate concentration of diesel exhaust involves optical measurements. This technique, however, suffers from a lack of accuracy and does not provide consistently reliable measurements of particulate mass. Another technique for measuring the particulate concentration of diesel exhaust involves forcing a measured amount of exhaust through a filter which collects the particulate therein, and then weighing the filter. The filter is preconditioned and preweighed so that the difference in weight of the filter before and after its use is representative of the amount of particulate within the exhaust. The disadvantage with this particular system is that it is extremely time consuming and labor intensive. Furthermore, the filter is not reusable after each measurement cycle thereby making it necessary to obtain a new filter for each diesel particulate measurement.
It is therefore an object of the present invention to provide a technique to accurately measure the particulate concentration of diesel exhaust.
It is also an object of the present invention to provide a technique for measuring the particulate concentration of diesel exhaust which is not labor intensive or time consuming.
It is also an object of the present invention to provide a technique for measuring the particulate concentration of diesel exhaust which utilizes a reusable filter or particulate collector to avoid the necessity of disposing of filters or collectors after they have been used to collect particulate.
It is also an object of the present invention to provide a technique for measuring the particulate concentration of diesel exhaust which provides consistently reliable readings.
It is also an object of the present invention to provide a technique to measure the concentration of non-volatile diesel particulate and/or volatile diesel particulate.
It is a further object of the present invention to provide a technique for measuring the carbon particulate level or concentration not only of diesel exhaust but also of other gaseous mixtures and samples.